Sonobuoys (short for sonar buoys) are sonar system devices, often but not always expendable, that can be deployed from airplanes and/or ships and are able to detect and possibly identify fixed and/or moving objects located under water. Detection sonobuoys, for example, listen for sound waves that reach its hydrophone or transducer (e.g., power and/or propeller noises from underwater vehicles and/or ships), emissions from moving parts contained in or disposed on underwater objects, power plant, propeller or door-closing and other noises, etc., from ships or submarines, or other acoustic signals of interest such as an aircraft black box pinger. The sonobuoy then transmits the detected information to a computer for processing (e.g., on an aircraft or vessel).
Sonobuoys have been used to provide a variety of functions, including but not limited to surveillance of underwater environments, antisubmarine warfare (ASW), communication with sea vessels and/or submarines, determining location of and/or tracking targets, locating underwater objects (both passive and active, the latter including aircraft black boxes), mapping natural and man-made underwater objects, locating and tracking fish and marine mammals, and measurement of characteristics relating to bodies of water, such as ocean currents, ocean temperature, ocean salinity, and wind speed. Typically a sonobuoy is designed to scuttle (sink) alter a predetermined time, or when a predetermined action/event occurs. U.S. Pat. Nos. 4,590,590, 4,654,832, 4,689,773, and 5,073,136 are exemplary sonobuoy patents and each of these is incorporated by reference.
There are various sizes (A, B, C, etc.) and types of sonobuoys (including active, passive, and special purpose), having various capabilities (measurement, Global Positioning system (GPS) enabled/equipped, controlled buoyancy, etc.). GPS-enabled/equipped sonobuoys can be active or passive, used for detection or measurement purposes, and are able to provide positioning information along with acoustic information. Some sonobuoy systems are implemented to be monostatic, meaning that the transmitter and receiver are in the same place. Bistatic sonar describes when the transmitter and receiver(s) are separated (e.g., by a distance large enough to be comparable to the distance to the target), and multistatic sonar is a multi-node system with more than one transmitter, receiver or both. For example, a deployed field that includes a plurality of appropriately spaced sonobuoys can be implemented as a multistatic sonar system, where the sonobuoys transmit signals and listen back for the echoes from the received signals (as well as for other acoustic sounds).
FIG. 1 is an illustrative block diagram of an exemplary prior art sonobuoy system 10. Sonobuoys 10 are often implemented as a self-contained package of electronics designed to be dropped into a body of water, enter into the water, detect underwater acoustic signals, and relay recorded information 17 about those underwater acoustic signals that it received back to a source device, such as a sonobuoy receiver 13 located on an aircraft 15 or shipping vessel (not shown). Sonobuoys 10 can be adapted to both detect and track underwater sounds, as well as measure ocean characteristics. Some sonobuoys 10, such as the one illustrated in FIG. 1, are designed to separate into two portions 12, 16 tethered together via a cable 14, including an underwater acoustic sensor portion 16 and a surface transmitter portion 12. The surface transmitter portion 12 floats in or on the water surface and receives, via the cable 14, the acoustic signals 19 detected by the underwater portion 16, and then transmits the detected acoustic signals 19 via transmitted radio signals 17 sent to a sonobuoy receiver 13 (shown for illustrative purposes only as being on an aircraft 15) for further processing and/or for viewing by a user (not shown).
As the above-referenced patents illustrate, sonobuoys 10 also can include a casing or outer canister that includes many additional components, such as a parachute, hydrophone, cable packs, floats, sea anchor, and the radio transmitter and associated antenna. Some of these are further explained below. As shown in the prior art example of FIG. 1, depending on the type of sonobuoys (e.g., passive, active, special purpose, etc.) a sonobuoy also can include one or more hydrophones 22, 28 or other transducers (e.g., the magnetic compass 26) to record information about underwater sounds and/or emit “pings” or sensors (not shown). If the sonobuoy 10 is a passive sonobuoy used for detection, the sonobuoy 10 includes one or more acoustic receivers (hydrophone) 22, 28 to detect acoustic energy emitted by remote sources. If the sonobuoy 10 is an active sonobuoy, it may also include one or more components usable to emit sound waves (not shown), wait for and detect the reflection back of the sound waves, and provide this data to the transmitter 20, to be uploaded to a sonobuoy receiver 13 that uses this data to gather information about objects (fixed and/or moving) in the water. Sonobuoys can be directional or non-directional as well: in a directional sonobuoy the directional receiver/hydrophone 22 detects energy from a limited angular field of view, whereas in a non-directional sonobuoy, the omnidirectional hydrophone 28 receives energy from all directions.
The sonobuoy 10 also includes a battery 30 capable of operation in water; for example, special types of batteries capable of being activated by presence in sea water are known in the art, such as sea water activated magnesium or silver chloride, lithium chemistry, and/or thermal batteries. In addition, controlled buoyancy sonobuoys, which can descend to a predetermined depth and then ascend back up to a different depth, are known in the art (see, e.g., U.S. Pat. Nos. 5,224,074 and 5,460,556, which are hereby incorporated by reference).
For sonobuoys used for detection of underwater sounds (e.g., submarine noise and fish sounds, sounds emitted from underwater objects like airplane black boxes, etc.), the hydrophone 28 or similar transducer detects the sound, and the detected sounds modulate an oscillator (not shown) in the RF transmitter portion 20 of the surface portion 12 of the sonobuoy 10. Optionally, the sonobuoy can include one or more amplifier or other electronics to amplify the detected sound. The RF transmitter 20 radio output is a frequency modulated signal (e.g., a very high frequency (VHF) or ultra-high frequency (UHF) band signal) that is transmitted from the VHF/UHF antenna 18, and the antenna signal 17 is received by a sonobuoy receiver 13 (e.g., on an aircraft 15 or ship (not shown)), and then detected and processed by a user or processor (not shown) having access to the sonobuoy receiver 13. For example, U.S. Navy sonobuoys use the VHF maritime mobile band (156.0 and 162.025 MHz, inclusive) to transmit sonobuoy data to an aircraft or ship, in frequency channels that can be about 375 kHz wide.
By analyzing information about the detected sounds that have been sent to the sonobuoy receiver 30, an operator, or a processor (or both), can determine various characteristics of the detected object(s). For example, in detection of submarines, several sonobuoys may be deployed in a tactical pattern, each sonobuoy using a different VHF or UHF frequency, enabling an operator or processing computer to localize, track, and classify a submerged submarine.
Special-purpose sonobuoys (also referred to as measurement sonobuoys) are another sonobuoy type and are not used for detection and generally do not include hydrophones or transducers. Rather, these types of sonobuoys (sometimes referred to as measurement sonobuoys) instead include one or more sensors to gather information about different ocean characteristics. Special purpose sonobuoys may, for example, include sensors configured to provide specific functions, such as measuring salinity of ocean water, water temperature, air temperature, barometric pressure, wave height, electric fields, magnetic anomalies, and bioluminescence (the light emitted by microscopic organisms disturbed by a passing submarine) marking the location of something at sea or under the sea, or assisting in communications occurring between aircraft and submarines.
Another device having some functions similar to a measurement/special purpose sonobuoy, is a dropsonde, which is an expendable weather reconnaissance device designed to be dropped from an aircraft at altitude to more accurately measure weather and storm conditions as the device falls to the surface (of the ocean or to land). The so-called “sonde” portion can include a GPS receiver, along with pressure, temperature, and humidity (PTH) sensors to capture atmospheric profiles and thermodynamic data. A dropsonde can relay these types of data to a computer in the aircraft by radio transmission. Dropsondes do not provide acoustic detection features and have no acoustic transmitter.